In "Year One," Zed (Jack Black), a hunter-gatherer-caveman type, complains that everyone takes a dump behind his hut. Having to sit through stinking, puerile dreck like this, I know how he feels -- metaphorically speaking, of course.

Civilization in has ground to a halt. Thousands of years of human achievement, and we're still obsessed with poop, pee, puke and fart jokes.

Actually, let's reduce that timeline a bit. In the 100 or so years since the invention of moving pictures, why, now, in the 21st century, are films still being made about two horny nincompoops on a road trip? Throw all the high-concept hooey you want at it -- in this case, two atavistic nitwits, Zed and Oh (Michael Cera), are cast from their tribe to make their way through the ancient world -- it's still the same flaccid, utterly pooped premise.

"Year One" is directed by Harold Ramis, who exhibits the desperation of a man trying to squeeze blood from this stone-age story. The elements for a laugh machine are here: Ramis is a Ghostbuster, and writer/director of "Groundhog Day." Black is a gifted physical comedian, often typecast as a slacker. Cera excels at trailing off at the end of a mumbled improvisation, often typecast as a dweeb.

This film puts the two actors in loincloths -- and Cera in a wig with bangs like a Quiet Riot bassist -- but they're still a slacker and a dweeb. Zed is a chubby hunter, scorned by the tough guys in the tribe. Oh is a willow-legged pantywaist who gathers strawberries for the fruit salad. Isn't this where survival of the fittest comes into play, where nature sends a pox or a predator to thin the herd?

Against all logic, they survive their exile and are subject to a crudely edited miscellany of adventures, studded with juvenile double-entendres and punctuated by the expulsion of bodily fluids. There's a flimsy thread of a theme here: Each new group of people they meet is progressively more civilized, and therefore, progressively more cruel and murderous. And by that, I mean each group is progressively more creative with its genital mutilation.

The screenplay strains to pervert biblical stories: Zed and Oh meet Cain (David Cross) and Abel (Paul Rudd), and we bear witness to the latter's death via big-rock-to-the-head. They run across Abraham (Hank Azaria), a circumcision-happy Jew, who puts his son Isaac (Christopher Mintz-Plasse) under the knife. Eventually, they make it to Sodom, lured by the promise of rampant prostitution; there, a grotesque high priest (Oliver Platt) tosses virgins into the fire and forces Oh to rub his chest with oil.

Dumb beyond all repair, "Year One" is absurdly primitive. There was no intelligent design in its creation. Its jokes are fossilized, unearthed by Ramis so 12-year-old boys can snicker at them. It's quite the waste of time and talent and swiftly crushes any hope that toilet humor would become a vestigial element of modern comedy.